Orthodontic correction of teeth for proper orientation generally requires the utilization of orthodontic braces which are designed to gradually force the teeth into a pre-determined corrected configuration. These braces are usually configured as tightly drawn wires attached to the teeth either peripherally on the external or visible side of the teeth or, for cosmetic reasons, against the internal surface of the teeth.
In order to keep the braces or wires in position, it is necessary to anchor the wires to a fixed position on the teeth and this is effected by means of dental bracket, i.e., wire holding brackets which are firmly attached to the surface of the teeth. In order to ensure that the brackets remain in position on the teeth, particularly with the constant stress placed on them, it is the practice to provide the bracket with a planar (i.e. loosely reflecting the shape of an average tooth surface) extension portion, or bottom, having a mesh brazed thereon and to which a tooth-conforming base material is attached. The base is closely conformed to a pre-selected portion of the tooth surface, which is rarely planar but is usually irregularly curved, and then the base, and the bracket, are adhered to the tooth. The conformed base assumes a full length area of attachment which the planar bracket itself cannot.
A common method for ensuring a proper attachment initially entails preparing a plaster of paris casting of the teeth. A hardened, molded base for fixing the dental bracket in place is then formed from the casting to serve as the base of the bracket, when it is applied to the tooth. The base is adhered to the bracket itself or to an extension of the bracket which is in the form of a mesh for enhanced bonding therebetween. The bracket and base are then adhered to the individual teeth.
The base, with attached bracket, is adhered to a tooth by a thin coating of a liquid dental adhesive which is brushed on one or both of the tooth surface and the engaging surface of the base, prior to actual use. The adhesive is a standard adhesive which, because of the preformed nature of the base, may be immediately adherent. While this method provides a well seated bracket, it requires additional steps and procedures in separately casting a mold prior to actual placement of the bracket on the tooth.
With a different and increasingly popular type of one step dental bracket, a dental bracket is provided, by welding thereto of a relatively rigid, generally tooth-conforming metal strip having a mesh thereon and onto which a relatively thick layer of a moldable, paste adhesive (as characterized by the manufacturer and which requires separate activation to permit for molding conformation prior to adhesion) has been loaded by the manufacturer. In use, the dental bracket is removed from its packaging, a release paper or plastic film is peeled off the manufacturer-applied adhesive surface, and the bracket base is pressed against the surface of the teeth to which it is to be adhered. The pre-loaded adhesive is relatively thick and moldable whereby compressive placement on the teeth causes the adhesive to conform to the normally irregular teeth surfaces and to fill in any gaps between the rigid base member and the teeth surfaces. Once the adhesive is properly conformed to a tooth, it is activated for adhesion (and hardened in place) by, for example, application of UV light irradiation to complete the adhesive placement of the bracket.
While such adhesive pre-loaded dental brackets are popular because of their convenience and simple application (even with use of a complementary adhesive which is often used on the teeth prior to the molded placement of the paste adhesive base), the use thereof requires the application of a relatively thick layer of paste adhesive, for molding conformity. This excessive thickness of adhesive layer however entails several drawbacks. As with adhesive application in any field, e.g., wood joints in carpentry, the weakest part of an adhesion bond between adhered rigid members, is the adhesive itself and accordingly thickness of the adhesive layer is usually minimized, where possible, for best and strongest adhesion properties. However, when the adhesive is thickened for a specific purpose, e.g., for gap filling, the integrity of the adhesive bond may be lessened. Thus, with the common adhesive pre-loaded dental brackets, the gap filling thickness of the adhesive (thicker than needed for adhesion), affords considerable stress points in the adhesive, at which the adhesive itself may split, with possible dislodgement of the bracket. If the base material has a greater shear strength than that of the adhesive, then use of a thickened adhesive layer works to reduce the overall integrity of the bond.
In addition and possibly of greater moment, is the fact that while application time may be initially lessened, this is more than offset by the additional labor and time required for the complete removal of the thick adhesive layer (at the time when the bracket is no longer needed, i.e., when the orthodontia is to be removed).